1. Field of the Invention
The present invention relates to an active matrix panel with a built-in data line drive circuit and to a display device using the panel.
2. Description of the Related Art
On an active matrix panel in which a polycrystal silicon is used for a channel of a thin film transistor (hereinafter referred to as TFT), pixel electrodes and TFTs for picture element which are provided correspondingly to the electrodes are arranged in the form of matrix, and a plurality of data lines and scanning lines are arranged according to the TFTs also in the form of matrix. A built-in drive circuit for supplying data signals and scanning signals to the data lines and the scanning lines is provided in the same active matrix panel on which the pixel TFTs are formed.
Examples of such built-in type conventional data line drive circuits are shown in FIGS. 1 and 2. In a data line drive circuit 1 as shown in FIG. 1, a series of RGB color video signals are input to the circuit which is composed of three color video signal lines 1R, 1G, and 1B for leading a series of RGB color video signals in a panel; switching elements 11, 21, 31 . . . for connecting data lines D1, D4, D7 . . . to the color video signal line 1R; switching elements 12, 22, 32 . . . for connecting data lines D2, D5, D8 . . . to the color video signal line 1G; switching elements 13, 23, 33 . . . for connecting data lines D3, D6, D9 . . . to the color video signal line 1B; and a drive pulse generating circuit comprising a shift register 4 for sequentially generating drive pulses PA1, PA2, PA3 . . . in response to clock signals CLKS. The drive pulse PA1 at the first stage of the shift register 4 is applied to the switching elements 11, 12, and 13, then the drive pulse PA2 at the next stage is applied to the switching elements 21, 22, and 23, and subsequently same processes are repeated, in other words, the respective identical drive pulses are applied to each three switching elements corresponding to the BRG color video signals.
At the exterior of the panel, as shown in FIG. 3, are provided a sample hold circuit 100 for a series of RGB color video signals which sequentially performs sampling of each RGB color video signal and simultaneously output hold signals for a prescribed period, and an inversion amplifier 200 which amplifies each of the RGB signals having gone through sample hold and outputs the signal after inverting it at every horizontal period and vertical period. It is arranged so that three outputs of the inversion amplifier 200 are input to the three color video signal lines 1R, 1G, and 1B in the panel.
Thus, when the drive pulse PA1 becomes high level, the switching elements 11, 12, and 13, which correspond to a series of RGB signals equivalent to three dots, are simultaneously turned on. Then, video signals input to the three color video signal lines 1R, 1G, and 1B are simultaneously supplied to the data lines D1, D2, and D3. Similarly, when the drive pulses PA2,
. . . Sequentially become high level, respective RGB video signals equivalent to three dots are simultaneously supplied to the data lines.
Here, the video signal lines 1R, 1G, and 1B have various parasitic capacities and line resistance, whereby video signals are delayed. In a circuit of a three dot corresponding system as shown in FIG. 3, new video signals are input to each of the video signal lines at intervals of three dots from an external sample hold circuit. Thus, for example, when a video signal three dots before is black level and a video signal three dots after is white level, when a delay of the video signal is great, a part of the black level is mixed with the white level three dots later, whereby a ghost of intermediate level may arise.
Such a ghost is negligible in displaying ordinary analog video signals for television or the like, but is very conspicuous when the display is used for displaying graphics. Thus, a circuit shown in FIG. 2 is occasionally used to prevent such ghosts from appearing.
A data line drive circuit 2 for inputting two series of RGB color video signals as shown in FIG. 2 is composed of six color video signal lines 1R, 1G, 1B, 2R, 2G, and 2B for leading two series of RGB color video signals in the panel; switching elements 11, 31 . . . for connecting data lines D1, D7 . . . to the color video signal line 1R; switching elements 12, 32 . . . for connecting data lines D2, D8 . . . to the color video signal line 1G; switching elements 13, 33 . . . for connecting data lines D3, D9 . . . to the color video signal line 1B; switching elements 21, 41 . . . for connecting data lines D4, D10 . . . to the color video signal line 2R; switching elements 22, 42 . . . for connecting data lines D5, D11 . . . to the color video signal line 2G; switching elements 23, 43 . . . for connecting data lines D6, D12 . . . to the color video signal line 2B; and a drive pulse generating circuit comprising a shift register 5 for sequentially generating drive pulses PB1, PB2, PB3 . . . in response to clock signals CLKs. The drive pulse PB1 at the first stage of the shift register 5 is applied to the switching elements 11, 12, 13, 21, 22, and 23, then the drive pulse PB2 at the next stage is applied to the switching elements 31, 32, 33, 41, 42, and 43, and subsequently same processes are repeated, in other words, the respective identical drive pulses are applied to each six switching elements corresponding to two series of RGB color video signals.
When graphics are displayed, a video signal to be input is typically an 8-bit-per-dot digital signal. At the exterior of the panel, there are provided a sample hold circuit 300 for two series of RGB signals which sequentially perform sampling of each series of RGB color video signals and simultaneously output hold signals equivalent to six dots for a prescribed period, a D/A converter 400 for converting digital signals equivalent to six dots supplied from the sample hold circuit 300 into analog signals, and an inversion amplifier 500 which amplifies the converted analog signals equivalent to six dots and outputs the signals after inverting them at every horizontal period and vertical period. It is arranged so that six outputs of the amplifier 500 are input to the six color video signal lines 1R, 1G, 1B, 2R, 2G, and 2B in the panel.
Thus, when the drive pulse PB1 becomes high level, the switching elements 11, 12, 13, 21, 22, and 23 which correspond to two series of RGB color video signals equivalent to six dots are simultaneously turned on, and video signals input to the six color video signal lines 1R, 1G, 1B, 2R, 2G, and 2B are then supplied simultaneously to the data lines D1, D2, D3, D4, D5, and D6. Similarly, when the drive pulses PA2, PB3 . . . sequentially become high level, respective RGB video signals equivalent to six dots are simultaneously supplied to the data lines.
With this constitution, new video signals are input to each of the video signal lines from an external sample hold circuit at intervals of six dots. Thus, even when a video signal six dots before is black level, a video signal six dots later is white level, and a delay of video signals is great, a part of the black level will not mix with the white level and ghost images can be prevented. Thus, such constitution of six dots corresponding system is optimum when graphic images are displayed.
As described above, a conventional three dots system circuit such as is shown in FIG. 1 is not sufficient for displaying graphics because such ghosts will arise. However, ghosts can be ignored when ordinary analog video signals are displayed and in such a system it is sufficient to have a series of external sample hold circuit. Thus, conventional circuit have advantages in terms of cost. On the other hand, a circuit of six dots system shown in FIG. 2 can prevent ghosts and is therefore suitable for displaying graphics. However, because a plurality of series of external sample hold circuits are required, this system makes it costly to display ordinary analog video signals. Thus, it is optimum that a circuit such as shown in FIG. 1 be used to display ordinary analog video signals and a circuit such as shown in FIG. 2 be used for graphic applications.
However, the circuits shown in FIGS. 1 and 2 differ not only in the constitution of the respective external sample hold circuit, but also in the constitution of the respective built-in data line drive circuits of the panels. Thus, different panels must be used to display ordinary analog video signals or graphics. In other words, two designs are required for the panels, and design and production costs are increased when two types of panels must be manufactured.